This does seem like a fundamental question. Jillian (the blogger from Sadly, No!) answers:
"Let’s help them out here, shall we? Banned Books Week is about censorship. If you don’t want your child to read a book, then you simply forbid them to check it out from the library. If they disobey you and read it anyway, then you have a parenting problem. "I remember reading "Catcher in the Rye" simply because it was on a banned book list, so perhaps I am not the one to address this. And not being a parent, I can't be too flip about this, but it does appear to be censoring for all, as opposed to saying "I don't want my kids to read this." It reminds me of school prayer where it sure seems like Christian parents (who already get to pray with their kids at home) are not so much wanting them to pray, but that heathen kid from down the street. And maybe it is my lack of parenting experience that makes me ask this, but why do parents fear that their kids will read one book and then reject their parental influence? Does it work that way?
Seriously, I want to know.